Cita APA (7th ed.)

Wang, H., & Whittington, D. (2000). Willingness to pay for air quality improvements in Sofia, Bulgaria. World Bank.

Cita Chicago (17th ed.)

Wang, Hua, i Dale Whittington. Willingness to Pay for Air Quality Improvements in Sofia, Bulgaria. Washington, D.C: World Bank, 2000.

Cita MLA (9th ed.)

Wang, Hua, i Dale Whittington. Willingness to Pay for Air Quality Improvements in Sofia, Bulgaria. World Bank, 2000.